1. Technical Field
Composite materials composed of cubic boron nitride (cBN) and a matrix component of various ceramic oxides, nitrides, and/or solid solutions of matrix materials thereof as well as carbide whiskers and methods of manufacturing thereof.
2. Description of the Related Art
Compositions of cutting tools having a majority of cubic boron nitride (cBN) phase (e.g. greater than 50 volume %) with various ceramic additions (such as oxides, nitrides, and carbides) have been commercialized for machining of cast iron, hardened steels, and other metals. However, the machining of certain cast iron alloys, such as ductile iron or composite graphite iron, presents difficulties due to the high temperatures generated from frictional heat during machining. It is believed that the high temperatures generated at the cutting point in some of these cast iron machining applications can lead to a chemical reaction between the iron and cBN, which is referred to as “chemical wear”. This in turn often leads to premature failure of the cutting tool.
Various compositions for cutting tools have been introduced in an attempt to address this problem. For example, alumina based cutting tools can potentially overcome the problem of chemical wear since alumina exhibits high chemical stability. However, alumina is prone to brittle fracture. Cutting tools composed of silicon nitride based ceramics, including solid solutions of silicon nitride, alumina, and aluminum nitride, such as the silicon aluminum oxynitrides phases have also been used for machining ferrous metals and alloys.[1-4] While their stability at high temperatures is beneficial, they do not possess the hardness and abrasion resistance exhibited by cBN containing cutting tools.
Additionally, fiber or whisker reinforcement is a strategy that has been pursued to impart greater fracture toughness to ceramic materials. As it relates to cutting tools designed for machining steel and iron, increased fracture toughness is a desirable attribute. For instance, it has been shown, in the case of alumina (Al2O3), that incorporation of whiskers of silicon carbide (SiC) [6-8] can significantly increase fracture toughness and lead to better performance in certain applications. SiC whiskers have been incorporated in a Si3N4,[9, 10] or AlN matrix.[11] SiC whiskers have also been added to Al2O3, mullite, or B4C (U.S. Pat. No. 4,543,345). Other whisker reinforcement methods[12, 13] and other whisker materials such as carbides, borides, and nitrides of titanium, zirconium, and other transition metals, have been reported.
Ceramic cutting tools reinforced by SiC whiskers, as well as other whisker materials, such as nitrides, borides, and carbides of transition metals (such as those of group 4 and 5) have been described. The incorporation of whisker reinforcements into a cBN ceramic by sintering has not been described. In particular, whiskers have not been incorporated into a ceramic matrix that also includes cBN. Nor has such a ceramic matrix including cBN and the dispersion of SiC whiskers homogeneously within the matrix or the maintenance of the integrity of the whiskers under the high pressures required for sintering cBN been described.
The disclosure contained herein describes attempts to address one or more of the problems described above. Accordingly, there is a need to provide a material that provides desired hardness, improved abrasion resistance, high temperature stability and resistance to chemical wear as well as for making a cutting tool that allows for faster cutting speeds.